Catalytic Liquefaction of Highly Inert Refining Residue over an Attapulgite-Supported Niobium Catalyst

Natural lignin would not be readily utilized due to its heterogeneity and structural complexity, moreover, the reactivity of the lignin that experienced the acid biorefinery process becomes lower. It has become a major issue to break the anti-degradation barriers of the highly inert acid-refining residue. A new strategy based on the design of attapulgite-supported niobium catalyst (ANC) was proposed to liquefy the acid-refining residue in water-ethanol co-solvent. Concentrated acid hydrolysis lignins (CAHLs), dilute acid hydrolysis lignins (DAHLs) and acid-enzymatic hydrolysis lignins (AEHLs) from different feedstocks, were prepared purposefully to evaluate the catalytic activity of ANC. All the highly inert residues could be efficaciously liquefied by ANC. The addition of niobium species significantly improved the yield of guaiacol and promoted the production of 4-methylcatechol. Reusability test suggested that ANC could be used at least five times. The results provide the possibility for the industrial application of this strategy.